Optional Mutagen

[ihor-sviziev]

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• Is there an existing issue that covers this? (link it here, if so)
• Is there an entry in the CHANGELOG.md file?

Describe the bug
This is a follow-up on #749
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• Matching PR in the documentation repo (replace text with link when it exists)
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[ihor-sviziev]

Hi @joseluisi4, @bap14,
I fixed all the issues listed in the pull request: #749.
However, I tested disabled mutagen with OMutagen on a quite big project (about 650 packages in composer)—the performance was almost the same but in some scenarios it was significantly slower than with Mutagen.

My measurements:

• Response time of frontend and admin - about 10% slower w/o Mutagen
• time (php bin/magento setup:upgrade) - about the same performance
• time (rm -Rf ./vendor/ && composer i) - about 50% slower w/o Mutagen
• time php bin/magento setup:di:compile - about 50% slower w/o Mutagen

So, I'm not sure if it's a good option to show a warning.

For myself, I decided that it's better to keep using Mutagen sync.

[diazwatson]

I think it is still good to give the option to devs

[navarr]

This looks good! I'll just need to dogfood it for a bit before merging